The ability of mucoadhesive polymers to swell is a prerequisite for mucoadhesion since it concerns wetting, uncoiling, and spreading of the polymer over the mucus (wetting theory). This spreading process, controlled by the interfacial properties of the mucus and mucoadhesive, allows intimate contact at the mucus-mucoadhesive interface, thus governing the formation of bonds (Lehr et al., 1992a, 1993). Over-hydrating of the polymer, however, may result in a slippery mucilage, deteriorating mucoadhesion (Mortazavi and Smart, 1993). Furthermore, swelling is a key-parameter for the environment-sensitive drug delivery (Qiu and Perk, 2001), where controlled drug release can be obtained by a reversible volume change of an environmental-sensitive polymer with controlled swelling-deswelling properties (Gutowska et al., 1997).

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